Benjamin w



(No Model.)

' B. W. PRENTIOE.

sEoTIoNAL EXPANSION TAP. No. 572,445. Patented Deo. 1, 1896.

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I BENJAMIN XV. PRENTICE, OF VOROESTER, MASSACHUSETTS, ASSIGNOR TO VERNON F. PRENTIOE AND ALBERT F. PRENTIOE, OF SAME PLACE.

SECTIOVNAL EXPANSION-TAP.,

SPECIFICATION forming part of Lettere Patent No. 572,445, dated December 1,1896. Application filed March l0, 1896. Serial No. 582,676. (No model.)

To a/ZZ whom/Vit may concer/c:

Be it known that I, BENJAMIN W. PREN- TICE, a citizen of the United States, residing at iVorcester, in the county of Worcester and State of Massachusetts, have invented a new and useful Sectional Expansion-Tap, of which the following, together with the accompanying drawings, is a specification sufficiently full, clear, and exact to enable persons skilled 1o in the art to which this invention appertains to make and use the same.

The object of my present invention is to provide a more eiicient and serviceable expansion tap or tool for accurately threading holes in machine-work; also, to provide an expansible tap comprising` a series of detachable sections and having means for retaining the said sections rigid upon their supporter or stem, and adapted for convenient adjust- 2o ment or expansion, as the cutting edges become Worn by use, for maintaining` the working diameter of Vthe tool at standard gage, as more fully hereinafter explained. These objects I attain by an expansion tap or instru- 2 5 ment constructed as shown in the drawings,

wherein- Figure lis a side view of a screw-threading tap embodying my invention. Fig. 2 is a 1ongitudinal sectional view in the direction of line 3o W' W, Fig. 3. Fig. 3 is a transverse section at line Fig. 2; and Fig. 4 is a view of the inner side of one of the working sections detached.

Referring to parts, A denotes the shaft, bar,

3 5 or stem, which may be of any desired length and of suitable diameter, according to the required size of tool. One end, a, is suitably tted for connection with the stock lor spindle of the drilling-machine or lathe in which the tool is to be used, and near its other end the stem A is formed slightly conical, or with a tapering exterior surface C, also with a screw-threaded end d at its smaller extremity, while a second screw-thread b is formed on the stem at the larger end of the tapered portion. Said tapered surface is provided with longitudinally-disposed keys or splines e, projecting therefrom, and screw-nuts B and D are arranged on the threaded portions b 5o and d of the stem.

F F F indicate a series of independent cylindiical segmental plates or working sections internally hollowed to seat at or near their edges upon the tapered portion O of the stem A. Each of said sections F is longitudinally grooved, as at m, to fit the splines or keys e, being free to slide endwise thereon, but held for rotation With the stem. The sections F are provided on their exterior with cutting edges f and intermediate grooves g, said edges 6o being litted with thread-cutting teeth for tapping purposes, or,rif for a reamer, the tool may be made with plain cutting edges in lieu of teeth. The ends of the sections F are fitted with conically-beveled surfaces o on their outer sides, and two ann ular cups or inwardlybeveled collars II and I are arranged on the stem A adjacent to the ends of the sections, their inwardlyconed surfaces 3 matching over. the beveled surfaces 5 of the sections, 7o thereby centering and rigidly holding the sections firmly in position when the nuts B and D are screwed up against the collars, as indicated.

In the present instancethe threading-cutters f on the tap are made dual between each of the respective clearing-grooves g, said cutters having formed therein a narrow inward incision or channel 6, extending across the threads and longitudinal with the axis of the 8o tap. The two portions at front and rear of said incision are each backwardly reduced or relieved, thereby providing a series of principal cutting-points f and a series of followers or secondary cutting-points f', that work 85 in adjacent succession thereto. This structure serves for steadyin g the action of the tap and giving greater efficiency in service, the

secondary cutting-point clearing the thread cut in case the primary point fails to fully do 9o its share of the work. This style of cutter for a tap is a feature of my invention.

Expansion ofthe tap is effected by adjust- ,ing the sections longitudinally along the tapered portion O of the stem toward the larger end of the taper. This is conveniently effected with the nuts B and D by easing back nut B and the collar H and forcing on the collar I by nut D, thereby increasing the working diameter of the tool to a degree corre- Ioo spending with the taper C of the stem, and this without deviation in destroying the partions F irmly to their central stem or support at any position of adjustment, and the splines or keys e insure their ix'e'dness laterally and their proper alinement With the axis of Athe stem. The Working sections can bereadily and accurately made by first constructing the group as a full cylinder and fthen vslitting the same into detached independent 'sections by longitudinal-cults on the desired lines of separation, as at 7.

As herein shown, the tap is made with vthree sections F, 'a preferable number; but a greater numberfo'f'seetions maybe employed as in any instance desired, the greater number being preferable in very large-sized taps.

I claim as my invention herein, to be secured vby Letters Patentl. The Within-describedl sectional expansion-tap, 'comprising in combination the axial stem formed with a tapered seat and having screw-threaded portions at either ends of the taper, the series of radially-projecting splines disposed longitudinally on said tapered seat, the series of independent .detachable segmental sections having conically-beveled ends, and straight edges that are adj ust-ably supported on said tapered seat, each section internally iitted with a longitudinal groove to receive the respective splines, and externally provided with cutting-points and clearance-grooves, as described, the internallybeveled annular collars mounted on the stem adjacent to and embracing the ends of the sev- Aeral sections, and the screw-nuts arranged upon the threaded stein adjacent to said c01- lars, all substantially as set forth.

2. In a screw-threading tap, the threadingcutters made in dualform, as shown with the narronT incision or 'channel 6 extending longitudinally of the body and dividing the raised portions 'of the thread cutter between the regular clearance-grooves into a series of primary 'cutting-po'ints and a series of secondary cutting-points, substantially as set forth.

Vitness my hand this 19th day of February, A.'D. 1896. 1

BENJAMIN lV. PRENTICE.

lVitnesses CHAs. H. BURLEIGH, SIMEON E. KING. 

